It was a welcome win only hours after the midlands club reassured the Football League they are not in financial difficulty and that they have the cash to complete the season.
Following eight games without a win, Birmingham carved out this victory as a result of an unfortunate 40th-minute own goal from Brentford centre-back James Tarkowski.
But they had to hang onto their slender lead after Stephen Gleeson was sent off in the 87th minute for stamping on Alex Pritchard.
Birmingham’s welcome win came following two heavy defeats during which time they had conceded eight goals.
Skipper Paul Robinson was dropped to the bench and on-loan Rob Kiernan from Wigan was drafted in, in an effort to shore up the defence.
A lethargic Birmingham, however, took some time to adjust against the promotion challengers but eventually settled down to produce some neat attacks.
Their best effort came from a move down the right which resulted in Paul Caddis swinging over a cross which Donaldson, the former Brentford striker, headed goalwards.
Goalkeeper David Button was alive to the situation and made a smart save at the far post.
This signalled a spell of attacking pressure and the talented teenager Demarai Gray should have done better from a David Cotterill corner as he blasted his effort high over the bar.
Andre Gray did no better a few minutes later when the stocky Brentford striker aimlessly lofted his cross shot high and wide.
Surprisingly Brentford struggled to get on top despite some skilful play by Pritchard. But no one was around to capitalise upon his smart play.
Pritchard did force Darren Randolph to make a stumbling save to his right to keep out a free-kick which penetrated Birmingham’s defensive wall.
The stalemate was broken in the 40th minute and came from a well-tested route. Birmingham’s skipper Caddis produced a low cross and Donaldson bravely dived low to head the ball which was unfortunately deflected into his own net by Tarkowski.
Brentford, however, wasted a glorious opportunity to equalise on the stroke of half-time when Jonathan Douglas carelessly headed Jon Toral’s cross over the bar.
Although they had most of the possession, Brentford ran headlong into a rugged Birmingham rearguard determined to hang onto their slender lead.
In the second period, Brentford strived to cancel out Birmingham’s advantage and dominated the exchanges.
They did leave themselves exposed to be caught on the break as highlighted when the unmarked Caddis went close to adding to their lead with a long-range effort which went just wide.
But the miss of the game fell to Demarai Gray in the 63rd minute.
Donaldson astutely knocked the ball back into the path of the unmarked youngster, who then conspired to shoot over the bar in front of an open goal.
Birmingham realised that they could test Brentford, with Cotterill forcing Button to make an excellent save with another long range effort.
Demarai Gray, keen to atone for his blatant miss, then produced an angled shot which was only just off target as Brentford’s exposed defence continued to live dangerously.
The equaliser eluded Brentford despite playing against 10 men after Gleeson was dismissed for stamping on Pritchard.